Is there a more influential conservative in Congress than Sen. Jim DeMint? The South Carolina Republican has emerged as a kingmaker in GOP nominating contests, irritating the party establishment by supporting conservative challengers against big-spending incumbents.

Mr. DeMint’s is the most coveted, though elusive, endorsement in his state’s pivotal presidential primary. He has been a leader in the fights over health care reform, the debt ceiling, the balanced-budget amendment and a whole host of other issues.

Jim DeMint is no Johnny-come-lately to the need for limited government and spending restraint. When other Republicans were going along with new regulations, the biggest new entitlement (entirely paid for with borrowed money) since the Great Society, and doubling the size of the Department of Education, Mr. DeMint said no and voted his conscience.

Now he has written an arresting new book, “Now or Never: Saving America From Economic Collapse.” His basic argument is that the country is saddled by crippling government debt and we don’t have much time to fix our fiscal imbalances. As President Reagan memorably asked, “If not now, when?”

Mr. DeMint divides the book into chapters describing the country’s economic problems, analyzing possible solutions and calling for decisive political action. Each chapter is preceded by an introduction written by a prominent conservative. Fellow senators - Tom Coburn, Patrick J. Toomey, Mike Lee and Marco Rubio - are contributors, as are former House Majority Leader Dick Armey and Rep. Steve King. Sen. Rand Paul writes the foreword.

This all-star cast should be unsurprising. Mr. DeMint aided Mr. Toomey, Mr. Lee, Mr. Rubio and Mr. Paul in their primary fights when many other Republicans feared they would be too right-wing. Now they are a powerful base of support on Capitol Hill for Mr. DeMint’s uncompromising brand of conservatism.

Some have criticized the book for using overly apocalyptic language. But what other words can be used when discussing a $15 trillion national debt that equals the size of the entire U.S. economy? Even this is a trifling figure compared to the unfunded liabilities of the major entitlement programs.

It has become a cliche to say every four years that the next election is the most important in our lifetimes. Yet the longer action is delayed, the deeper the federal government is in the hole and the more drastic become the possible solutions. Thus, those who pose as defenders of the social safety net as they stand in the way of entitlement reform may be, in fact, complicit in the safety net’s shredding.

While the book primarily is about the fiscal and economic challenges that lie ahead, Mr. DeMint does not call for a social-issues truce while we confront what Indiana Gov. Mitch Daniels has called the new “Red Menace” of red ink. He argues that economic and social conservatism cannot be separated.

“Some politicians have suggested that social issues be set aside while we address our fiscal crisis, but this view belies the real root causes of the nation’s reckless spending and crushing debt,” Mr. DeMint writes. “Cultural pathologies caused by the unintended consequences of naive social policies have contributed to many of America’s economic and fiscal problems.”

Ultimately, Mr. DeMint contends, we have no choice but to rein in federal spending, unleash the productive private sector and encourage strong values. Above all else, he writes that Congress must take seriously its oath to uphold the Constitution, noting that “the explicit functions of the federal government are found in Article I, Section 8.” If more of Mr. DeMint’s colleagues had voted accordingly, the crisis he laments could have been averted.

It may not be morning in America anymore. But it’s still not too late.